Polyamide fibers, fiber structure using same, and clothing

ABSTRACT

Disclosed is a polyamide fiber having a degree of orientation equal to or higher than 0.7 and equal to or lower than 0.85. The polyamide fiber is suitably obtained by forming a polyamide component having high moisture absorbency and a specific soluble component into a conjugated fiber under specific fiber formation conditions.

TECHNICAL FIELD

The present invention relates to a polyamide fiber for forming, forexample, clothing for sports and underwear, and a fiber structure formedusing the polyamide fiber.

BACKGROUND ART

Known synthetic fibers, for example, polyester fibers, and polyamidefibers such as nylon-6 and nylon-6,6, are used not only for clothing,but also for a wide range of industrial purposes due to their goodphysical and chemical properties. These fibers are of high industrialvalue.

Unfortunately, these synthetic fibers are low in moisture absorbency andwater absorbency, which actually limits their applications to clothingwhich are required to be absorbent of moisture and water, such asunderwear, intermediate garment, bed sheets, and towels. In view ofthis, for polyester fibers, for example, some methods have been proposedfor improving the low moisture absorbency and water absorbency, whichcan be referred to as the main shortcoming of the polyester fibers.

More specifically, the proposed methods include, for example, a methodin which polyester fibers are post-treated using a hydrophilicpost-processing agent, and a method in which polyester fibers are causedto have pores in their surfaces or interiors to obtain moistureabsorbency and water absorbency. However, according to these methods,the moisture absorbency and water absorbency are insufficientlyimproved, and the properties provided to the fibers are deteriorated bywashing.

Some methods have been proposed to solve the above problems. Accordingto such methods, an ethylene-vinyl alcohol-based copolymer, which isobtained by saponifying an ethylene-vinyl acetate-based copolymer, isconjugated with another thermoplastic polymer such as polyester,polyamide, or polyolefin, and the resultant conjugated material isformed into fibers, thereby improving dimensional stability (see, forexample, Patent Documents 1-3).

CITATION LIST Patent Documents

Patent Document 1: Japanese Examined Utility Model Publication No.S56-005846

Patent Document 2: Japanese Examined Utility Model Publication No.S55-001372

Patent Document 3: Japanese Examined Utility Model Publication No.H07-084681

SUMMARY OF THE INVENTION Technical Problem

However, the ethylene-vinyl alcohol-based copolymer according to theabove-described known techniques has insufficient resistance to moistheat, which disadvantageously limits its applications.

Meanwhile, regarding nylon fibers used in underwear, socks, and otherclothing, it is difficult to improve comfort of a fiber structure andclothing containing nylon fibers sufficiently by simply providing thenylon fibers themselves with moisture absorbency. Therefore, there is anincreasing demand for moisture-absorbing, and water-absorbing extensiblefibers capable of controlling humidity.

In view of the foregoing background, it is therefore an object of thepresent invention to provide a highly moisture-absorbent polyamide fiberwhich extends and contracts significantly in a reversible manner uponabsorbing and releasing water, and from which a highly comfortable fiberstructure can be produced. The present invention also aims to provide afiber structure and clothing which are formed using the polyamide fiber.

Solution to the Problem

To achieve the object, a polyamide fiber of the present invention has adegree of orientation equal to or higher than 0.7 and equal to or lowerthan 0.85.

Advantages of the Invention

The present invention provides a fiber structure which controls humidityhighly effectively and provides more comfort than ever.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of an exemplary cross section of a conjugatedfiber for obtaining a fiber of the present invention.

FIG. 2 is a photograph of an exemplary cross section of a conjugatedfiber for obtaining a fiber of the present invention.

FIG. 3 is a photograph of an exemplary cross section of a conjugatedfiber for obtaining a fiber of the present invention.

FIG. 4 is a photograph of an exemplary cross section of a conjugatedfiber for obtaining a fiber of the present invention.

DESCRIPTION OF EMBODIMENTS

A polyamide fiber of the present invention has a degree of orientationequal to or higher than 0.7 and equal to or lower than 0.85. If thedegree of orientation were lower than 0.7, sufficient colorfast couldnot be obtained. If the degree of orientation were higher than 0.85, thefiber would reversibly extend and contract in an insufficient mannerupon absorbing and releasing water. This would cause the stitches inwoven or knitted fabric to open and close insufficiently and make itimpossible to obtain a highly comfortable fiber structure.

Thus, a fiber structure such as woven or knitted fabric is producedusing the polyamide fibers having a degree of orientation equal to orhigher than 0.7 and equal to or lower than 0.85. When absorbing sweat,for example, the polyamide fibers extend to cause the stitches in thewoven or knitted fabric to open, thereby releasing humidity inside theclothing. When dried, the polyamide fibers contract to restore theoriginal length and cause the stitches to close, thereby preventing heatfrom being released outside the clothing. Thus, the use of the polyamidefibers of the present invention may provide woven or knitted fabricwhich is highly comfortable and has a so-called self-control function.

Note that the degree of orientation of the polyamide fiber isbeneficially equal to or higher than 0.72, and more beneficially equalto or higher than 0.75. Further, the degree of orientation of thepolyamide fiber is beneficially equal to or lower than 0.83, morebeneficially equal to or lower than 0.8, and still more beneficiallylower than 0.80. The degree of orientation of the polyamide resin iscalculated by a measurement method which will be described later withreference to examples.

The polyamide fiber of the present invention beneficially has a moistureabsorption rate equal to or higher than 5% at a temperature of 35° C.and a humidity of 95% RH, and a water absorption extension rate equal toor higher than 5% at a temperature of 20° C. and a humidity of 65% RH. Amoisture absorption rate lower than 5% would cause a user to feelstickiness and sweatiness. A water absorption extension rate lower than5% would cause the fiber to reversibly extend and contract in aninsufficient manner upon absorbing and releasing, and would preventstitches in woven or knitted fabric from opening and closingsufficiently. Such moisture absorption rate and water absorptionextension rate make it impossible to obtain a highly comfortable fiberstructure.

Thus, the use of the polyamide fiber having the above-specified moistureabsorption rate and water absorption extension rate may enable theproduction of a fiber structure such as woven or knitted fabric, whichhas the self-control function described above and provides more comfort.

Excessive increases in the moisture absorption rate and the waterabsorption extension rate tend to reduce wash-fastness, weatherresistance, light resistance, and chemical resistance, for example. Inview of this, the moisture absorption rate is beneficially equal to orhigher than 5% and equal to or lower than 30%, and more beneficiallyequal to or higher than 8% and equal to or lower than 25%. The waterabsorption extension rate is beneficially equal to or higher than 5%,more beneficially equal to or higher than 7%, still more beneficiallyequal to or higher than 8%, and particularly beneficially equal to orhigher than 10%. Further, the water absorption extension rate isbeneficially equal to or lower than 30%, more beneficially equal to orlower than 25%, and still more beneficially equal to or lower than 20%.The moisture absorption rate and the water absorption extension rate ofthe polyamide resin are measured according to a measurement method whichwill be described later with reference to the examples.

The polyamide fiber has a crimp extension rate which is beneficiallyequal to or higher than 1.5% and equal to or lower than 10%, morebeneficially equal to or higher than 2% and equal to or lower than 8%,and still more beneficially equal to or higher than 2.5% and equal to orlower than 5.8%. A crimp extension rate equal to or higher than 1.5% andequal to or lower than 10% provides silk-like feel and texture, andmakes fabric soft and pleasant to the touch.

Examples of the polyamide to be used in the present invention include:polycaproamide (nylon-6), poly-w-aminoheptanoic acid (nylon-7),polyundecaneamide (nylon-11), polyethylene diamine adipamide(nylon-2,6), polytetramethylene adipamide (nylon-4,6), polyhexamethyleneadipamide (nylon-6,6), polyhexamethylene sebacamide (nylon-2,10),polyhexamethylene dodecamide (nylon-6,12), polyoctamethylene adipamide(nylon-8,6), polydecanomethylene adipamide (nylon-10,6), andpolydodecamethylene sebacamide (nylon-10,8). Examples of the polyamidefurther include: caprolactam/lauric lactam copolymer (nylon-6/12),caprolactam/w-aminononanoic acid copolymer (nylon-6/9),caprolactam/hexamethylene adipate copolymer (nylon-6/6,6), lauriclactam/hexamethylene diamine adipate copolymer (nylon-12/6,6),hexamethylene diamine adipate/hexamethylene diamine sebacate copolymer(nylon-6,6/6,10), ethylenediamine adipate/hexamethylene diamine adipatecopolymer (nylon-2,6/6,6), and caprolactam/hexamethylene diamineadipate/hexamethylene di amine sebacate copolymer (nylon-6,6/6,10).

Among these substances, nylon-6 and nylon-6,6 are most suitable as thepolyamide of the present invention. Nylon-6 is still more beneficialbecause it is unexpansive and versatile, and has high moistureabsorbency. Among the above copolymers, nylon-6/6,6 and nylon-6/12 arebeneficial. Although the composition ratio between the component havinga carbon number of 6 and the component having a carbon number of 12 thatform the nylon-6/12 is not particularly limited, the component having acarbon number of 12 beneficially constitutes 50 mol % or less, and morebeneficially 40 mol % or less.

The polyamide copolymers may be caused to contain an anti-static agent,a lubricant, an anti-blocking agent, a stabilizer, a dye, or a pigment,for example.

The polyamide fiber of the present invention may be produced by anymethod as long as the polyamide fiber has the above-described degree oforientation, moisture absorption rate, and water absorption extensionrate. For example, a polyamide component (component A) and anothersoluble component (component B) are formed into a conjugated fiber, andthereafter, the component B is dissolved and removed, thereby suitablyproducing the polyamide fiber of the present invention. The use of sucha conjugated fiber enables the control of the structure of the polyamidecomponent, thereby enabling the production of a fiber which isexclusively made of polyamide, has a specific degree of orientation,high moisture absorbency and high water absorption extensibility, and iscapable of reversibly extending and contracting upon absorbing andreleasing water.

If the polyamide fiber of the present invention is produced from theconjugated fiber as described above, the other component, i.e., thesoluble component (component B) plays an important role in the structurecontrol. An exemplary polymer which can be used as the component B is awater-soluble thermoplastic polyvinyl alcohol-based polymer. Thispolyvinyl alcohol-based polymer beneficially has a viscosity averagedegree of polymerization of 200-500, a degree of saponification of90-99.99 mol %, and a melting point of 160-230° C. Although thepolyvinyl alcohol-based polymer may be a monopolymer or a copolymer, itis recommended to use a copolymerized polyvinyl alcohol which is 0.1-20mol % modified by α-olefin having a carbon number of 4 or less such asethylene or propylene, in order to ensure ease of melt spinning, watersolubility, and fiber physical properties. The polyamide fiber of thepresent invention can be suitably obtained by removing, by using hotwater, the water-soluble thermoplastic polyvinyl alcohol-based polymerfrom the conjugated fiber including the component B.

A polyester-based polymer which is soluble in alkali at a high speed(easily alkali-soluble polyester-based polymer) is another example whichcan be used as the component B. Examples of such an easilyalkali-soluble polyester-based polymer include a polylactic acid, andcopolymerized polyester formed by copolymerizing 1-5 mol % of 5-sodiumsulfoisophthalic acid, 5-30 wt. % of polyalkylene glycol, aconventionally used diol component, and a conventionally useddicarboxylic acid component. From a conjugated fiber containing thiscomponent B, the polyamide fiber of the present invention may besuitably obtained by the removal of the easily alkali-solublepolyester-based polymer by alkaline treatment.

It is beneficial that the conjugated fiber for producing the polyamidefiber of the present invention has a fiber cross section of which 50% ormore is coated with the soluble component (component B). It is morebeneficial that the entire cross section is coated with the solublecomponent (component B). That is to say, the conjugated fiberbeneficially has a sheath-core cross section in which the polyamidecomponent forms the core and the component B forms the sheath, or asea-island cross section in which the polyamide component forms theislands and the component B forms the sea.

A conjugate ratio (A:B) of the conjugated fiber of the present inventionbetween the polyamide component (A component) and the soluble component(B component) ranges beneficially from 90:10 to 40:60 (weight ratio),and more beneficially from 80:20 to 60:40 (weight ratio). The ratio maybe adjusted according to fiber shapes. Note that if the component B isused in a small amount, it may become difficult to control the polyamidestructure. This may makes it impossible to achieve desired moistureabsorbency and water absorption extensibility, resulting in difficultyin humidity control.

The cross section of the conjugated fiber of the present invention isnot particularly limited, provided that the component B is dissolved andremoved by hot water treatment or alkali treatment, and cracks are notcaused in the component A. The cross section may be of a concentric,eccentric, or multi-centric type, for example. Further, the crosssection may have, besides the circular shape shown in FIGS. 1 and 2, amultifoil shape shown in FIG. 3, or a modified shape such as a triangleor flat shape. Furthermore, as shown in FIG. 4, the component A mayinclude therein a hollow portion. The cross section may have one ormultiple hollow portions, without causing any problem.

The polyamide fiber of the present invention may beneficially have amonofilament size of 0.03-10 dtex, which is not limiting. The polyamidefiber of the present invention may be used not only as a long fiber, butalso as a short fiber or a short-cut fiber.

Once a combination of a polyamide component (component A) and the othercomponent, i.e., the soluble component (component B), is determined, theconjugated fiber of the present invention may be formed by using a knownconjugated fiber-spinning machine.

Setting of fiber formation conditions is important to obtain the fiberof the present invention. It is most suitable to form the fiber bydirect spinning and drawing method at a high speed. If the fiber is meltspun at a low or intermediate speed, and subjected to drawingthereafter, the temperature of heat treatment for the drawing is set toa temperature lower than 100° C., and beneficially to 80° C. or lower,and the drawing rate is set to a rate lower than 2. If drawing and falsetwisting are performed at the same time or continuously after thespinning, the temperature of the heat treatment is also set to atemperature lower than 100° C., and beneficially to 80° C. or lower, andthe drawing rate is limited to a rate lower than 2. If the temperaturewere set to 100° C. or higher, or if the drawing rate were set to 2 orhigher, it would be difficult to control the polyamide structure, anddesired degree of orientation, moisture absorbency, and water absorptionextensibility could not be achieved.

The polyamide fiber of the present invention may be used to form varioustypes of fiber structures (fiber aggregates). Here, the “fiberstructure” may be configured as a multifilament thread, a spun yarn,woven or knitted fabric, non-woven fabric, paper, synthetic leather, andwadding which are exclusively made of the polyamide fiber of the presentinvention. Alternatively, the “fiber structure” may be configured as:woven or knitted fabric or non-woven fabric, part of which is made ofthe polyamide fiber of the present invention; combined woven or knittedfabric additionally containing fibers of a different type such asnatural fibers, artificial fibers, synthetic fibers, or semi syntheticfibers; and woven or knitted fabric, cotton-containing non-woven fabric,or fiber layered product in which the polyamide fibers of the presentinvention are used as a finished yarn such as a blended yarn, adoubling-and-twisted yarn, a confound yarn, or a crimp yarn.

The weight ratio of the polyamide fiber of the present invention withrespect to the entire woven or knitted fabric or non-woven fabric isbeneficially 15 wt. % or more, more beneficially 18 wt. % or more,particularly beneficially 23 wt. % or more. After woven or knitted intofabric, or formed into a non-woven fabric, the fibers of the presentinvention may be subjected to napping treatment by means of wire raisingor any other finishing.

If the polyamide fiber of the present invention is produced via theconjugated fiber described above, a fiber structure may be formed usingthe fiber which contains polyamide alone and from which the component Bhas been removed. Alternatively, the component B may be removed from afiber structure which has been formed using the conjugated fiber.

EXAMPLES

The present invention will be described more specifically below withreference to examples.

Example 1

(Production of Polyamide Fibers)

Nylon-6 having a reduced viscosity of 1.80 dL/g (at a concentration of 1g/dL in orthoclorophenol at 30° C.) was used as a polyamide component(component A), and a thermoplastic modified polyvinyl alcohol (modifiedPVA) (product of Kuraray Co., Ltd. having a saponification degree of98.5, an ethylene content of 8.0 mol %, and a degree of polymerizationof 390) was used as a soluble component (component B). The components Aand B were separately melted in different extruders, and a conjugatedfiber having a cross section shown in FIG. 1 was injected through amulti-component fiber-spinning nozzle with a ratio of nylon-6:modifiedPVA set at 60:40 (weight ratio). Subsequently, a thread injected througha spinneret was cooled using a horizontal cooling air blower having alength of 1.0 m. Thereafter, water-free spinning oil including, as itscomponents, an anti-static agent and a lubricating agent was applied tothe thread. The thread was then wound using a roller at a take-off speedof 3500 m/min. In this manner, a conjugated fiber (111 dtex/24filaments) was produced. Note that the process steps of fiber productionwere performed smoothly. The produced conjugated fiber was knitted intocylindrical fabric by a circular knitting machine (28 gauge). Theresultant knitted fabric was subjected to a scouring step using hotwater (90° C., 20 minutes) to dissolve and remove the modified PVA. Inthis manner, the polyamide fiber of the present invention was produced.

(Measurement of Degree of Orientation)

Next, the degree of orientation of the produced polyamide fiber wasmeasured by using the following measurement device under the followingmeasurement conditions.

Measurement device: a two dimensional detector-equipped X-raydiffractometer (product of Bruker AXS K.K., product name; “D8 Discoverwith GADDS”)

Detector: Two-dimensional PSPC•Hi-STAR Measurement conditions: a currentof 110 mA; a voltage of 45 kV; a camera distance of 15 cm; a collimatordiameter of 0.5 mm; an exposure time of 1200 sec.; 2θ axis at 22°; ωaxis at 0°; and χ axis at 90° (equator line)•0° (meridian)

A single yarn was used as the sample. The angle of the χ axis wasadjusted such that the sample is positioned perpendicularly to theequator line and parallel to the meridian.

Thereafter, two-dimensional data in the meridian direction obtained inthe foregoing manner was converted to an X-ray diffraction intensitycurve in an azimuthal direction under the following conditions.

2θ=9.7°-11.7°,χ=−150°-−30°,step width=0.1°

Finally, the half-power bandwidth (Wi(°)) of an intensity map obtainedin the above manner was found. The degree of orientation of the fiberwas calculated by a simple method according to the following expression:

Degree of orientation: A=(360−ΣWi)/360

(Measurement of Moisture Absorption Rate)

Next, the produced polyamide fiber was maintained in a thermo-hygrostatchamber regulated at 35° C. and 90% RH for 24-hour humidity regulation.The moisture absorption rate of the fiber was then calculated based onan absolute dry sample weight and a humidity-regulated sample weight,according to the following expression. The results are shown in Table 1.

Moisture absorption rate (%)=(humidity-regulated sample weight−absolutedry sample weight)×100/absolute dry sample weight

(Measurement of Water Absorption Extension Rate)

The produced polyamide fiber was wound into a hank, and the hank wastreated at no tension and in boiling water for 30 minutes. Thereafter,the hank was air-dried at a temperature of 20° C. and a humidity of 65%RH, thereby regulating the humidity. The thread was then subjected to adry heat treatment for two minutes in an atmosphere at 160° C., at notension, and in a contactless fashion. Then, the thread was left in anatmosphere at a temperature of 20° C. and a humidity of 65% RH for 24hours. After the lapse of 24 hours, the length of the thread with a loadof 0.88×10⁻³ cN/dtex applied thereto was measured. This length isreferred to as “the thread length in dry state.” Thereafter, the threadwas immersed in softened water having a temperature adjusted to 20° C.for one minute. The thread was then raised from the water, sandwichedbetween two sheets of filter paper which had been air-dried in anatmosphere at a temperature of 20° C. and a humidity of 65% RH, andplaced on a flat table. A weight of 1.5 g/cm² was put and left over thethread for two seconds to remove excessive moisture on the fibersurface. After 10 seconds, the length of the thread was measured with aload of 0.88×10⁻³ cN/dtex applied thereto. This length is referred to as“the thread length in water absorption state.” The water absorptionextension rate of the polyamide resin was calculated according to thefollowing expression. Note that all the measurements were performed inan atmosphere at a temperature of 20° C. and a humidity of 65% RH.

Water absorption extension rate (%)=(“Thread length in water absorptionstate”−“Thread length in dry state”)/“Thread length in dry state”×100

(Evaluation Through Wear Test)

The produced polyamide fiber was knitted into some pieces of cylindricalknitted fabric by a circular knitting machine. Ten arbitrarily chosentesters passed one day with the resultant pieces put on their elbows andknees. The testers made sensory evaluation concerning feeling ofstickiness and sweatiness. The results of the sensory evaluation werequalified in terms of points: “No feeling of stickiness or sweatinessand highly comfortable” was qualified as two points, “Comfortable” asone point, and “uncomfortable” as 0 point.

The pieces of the knitted fabric were evaluated and classified into thefollowing four levels according to the total sums of points. Table 1shows the results.

A: 15 points or more in total

B: 8-14 points in total

C: 5-7 points in total

D: 4 points or less in total

(Measurement of Crimp Extension Rate)

The polyamide fiber was wound into a small hank having 20 turns by usinga sizing reel of which the frame perimeter was 1.125 m. The resultantsmall hank was heat-treated in boiling water at 98° C. for five minuteswith no load applied to the hank. The small hank was then left in achamber at constant temperature and humidity (at a temperature of 20±2°C. and a relative humidity of 65±2%) for 24 hours. A load of 2 mg/d wasapplied to the humidity-regulated fiber, and the hank length L₁ wasmeasured after one minute. Next, a load of 0.1 g/d was applied to thesmall hank, and the hank length L₂ was measured after one minute. Thecrimp extension rate is given by the following expression:

Crimp extension rate (%)=(L2−L1)/L2×100

Here, “g/d” represents a number of grams per denier.

Table 1 shows the results of these measurements and evaluation.

Example 2

A polyamide fiber was produced in the same manner as in Example 1,except that polyethylene terephthalate (copolymerized PET) having alimiting viscosity number [1] of 0.52 dL/g and copolymerized with 8 wt.% of polyethylene glycol having a molecular weight of 2000 and 5 mol %of 5-sodium sulfoisophthalic acid was used as the component B. Thedegree of orientation, the moisture absorption rate, the waterabsorption extension rate, and the crimp extension rate of thispolyamide fiber were measured, and the evaluation of knitted fabric ofthe fiber was performed through a wear test. The results of thesemeasurements and evaluation are shown in Table 1.

Examples 3 and 4

As shown in Table 1, a polyamide fiber of each of these examples wasproduced in the same manner as in Example 1, except that nylon-6,6(Example 3) or nylon-6/12 (Example 4) was used as the component A. Foreach fiber, the degree of orientation, the moisture absorption rate, thewater absorption extension rate, and the crimp extension rate weremeasured, and the evaluation of knitted fabric of each fiber wasperformed through a wear test. The results of these measurements andevaluation are shown in Table 1.

Examples 5 and 6

As shown in Table 1, a polyamide fiber of each of these examples wasproduced in the same manner as in Example 1, except that the conjugatedfiber was caused to have a cross section shown in FIG. 2 (Example 5) ora cross section shown in FIG. 4 (Example 6). For each fiber, the degreeof orientation, the moisture absorption rate, the water absorptionextension rate, and the crimp extension rate were measured, and theevaluation of knitted fabric of each fiber was performed through a weartest. The results of these measurements and evaluation are shown inTable 1.

Comparative Example 1

A polyamide fiber was produced in the same manner as in Example 1,except that the soluble component (component B) was omitted. The degreeof orientation, the moisture absorption rate, the water absorptionextension rate, and the crimp extension rate of this fiber weremeasured, and the evaluation of knitted fabric of the fiber wasperformed through a wear test. The results of these measurements andevaluation are shown in Table 1.

Comparative Example 2

A conjugated fiber (size: 275 dtex) having a cross section shown in FIG.1 was injected through a multi-component fiber spinning nozzle, in thesame manner as in Example 1. Subsequently, a thread injected from aspinneret was cooled using a horizontal cooling air blower having alength of 1.0 m. Thereafter, water-free spinning oil including, as itscomponents, an anti-static agent and a lubricating agent was applied tothe thread. The thread was then taken off using a roller at a speed of1000 m/min., and drawn continuously without being wound. The thread wasdrawn until its length became 2.5 times as long as the original length,while being thermo-set at 150° C. In this manner, a conjugated fiber(110 dtex/24 filaments) was produced at a speed of 2500 m/min. Theproduced conjugated fiber was knitted into cylindrical fabric by acircular knitting machine (28 gauge). The resultant knitted fabric wassubjected to a scouring step using hot water (90° C., 20 minutes) todissolve and remove the modified PVA. In this manner, the polyamidefiber of this comparative example was produced.

Next, the degree of orientation and the water absorption extension rateof the polyamide fiber were measured, and the evaluation of knittedfabric of the fiber was performed through a wear test, in the samemanner as in Example 1. Note that the moisture absorption rate and thecrimp extension rate were not measured. The results of thesemeasurements and evaluation are shown in Table 1.

Comparative Example 3

A polyamide fiber was produced in the same manner as in Example 1,except that nylon-12 was used as the component A. The degree oforientation and the water absorption extension rate of this polyamidefiber were measured, and the evaluation of knitted of the fiber wasperformed through a wear test. Note that the moisture absorption rateand the crimp extension rate were not measured. The results of thesemeasurements and evaluation are shown in Table 1.

Comparative Example 4

A conjugated fiber (size: 275 dtex) having a cross section shown in FIG.1 was injected through a multi-component fiber spinning nozzle, in thesame manner as in Example 1. Subsequently, a thread injected through aspinneret was cooled using a horizontal cooling air blower having alength of 1.0 m. Thereafter, water-free spinning oil including, as itscomponents, an anti-static agent and a lubricating agent was applied tothe thread. The thread was then taken off using a roller at a speed of2000 m/min., thereby obtaining undrawn thread. The obtained undrawnthread was knitted into cylindrical fabric by a circular knittingmachine (28 gauge). The resultant knitted fabric was subjected to ascouring step using hot water (90° C., 20 minutes) to dissolve andremove the modified PVA. In this manner, the polyamide fiber of thiscomparative example was produced.

Next, the degree of orientation and the water absorption extension ofthis polyamide fiber were measured, and the evaluation of knitted fabricof the fiber was performed through a wear test in the same manner as inExample 1. Note that the moisture absorption rate and the crimpextension rate were not measured. The results of these measurements andevaluation are shown in Table 1.

TABLE 1 Polyamide Soluble Conjugate Moisture Water Absorption EvaluationCrimp Component Component Ratio Cross Degree of Absorption ExtensionRate through Extension (Component A) (Component B) A:B SectionOrientation Rate (%) (%) Wear Test Rate (%) Example 1 Nylon-6 ModifiedPVA 60:40 FIG. 1 0.78 9 11 A 4.8 Example 2 Nylon-6 Copolymerized PET60:40 FIG. 1 0.84 7 5 B 3.6 Example 3 Nylon-6.6 Modified PVA 60:40 FIG.1 0.75 9 11 A 5.3 Example 4 Nylon-6/12 Modified PVA 60:40 FIG. 1 0.74 88 B 4.5 Example 5 Nylon-6 Modified PVA 60:40 FIG. 2 0.7 10 13 A 5.8Example 6 Nylon-6 Modified PVA 60:40 FIG. 4 0.8 6 9 A 2.8 ComparativeNylon-6 — — Circular 0.95 3 8 D 1.3 Example 1 Comparative Nylon-6Modified PVA 60:40 FIG. 1 0.88 — 2 C — Example 2 Comparative Nylon-12Modified PVA 60:40 FIG. 1 0.9 — 0 D — Example 3 Comparative Nylon-6Modified PVA 60:40 FIG. 1 0.5 — 32 D — Example 4

As shown in Table 1, the polyamide fibers of Examples 1-6 have a degreeof orientation equal to or higher than 0.7 and equal to or lower than0.85. Therefore, these fibers have a water absorption extension rate of5% or more at a temperature of 20° C. and a humidity of 65% RH. Thismeans that these polyamide fibers effectively control humidity, andknitted fabric made of these fibers is highly comfortable when worn.

On the other hand, the polyamide fibers of Comparative Examples 1-3 havea degree of orientation equal to or higher than 0.85. Therefore, thesefibers have a water absorption extension rate lower than 5% at atemperature of 20° C. and a humidity of 65% RH. This means that thesefibers control humidity less effectively and the knitted fabric made ofthe fibers of these comparative examples is notably uncomfortable whenworn, as compared to the fibers of Examples 1-6. In particular, nylon-12used in Comparative Example 3 is highly hydrophobic and has a highcrystal orientation among polyamide resin. Consequently, the fiber ofComparative Example 3 has a high degree of orientation as shown in Table1, which means that the obtained knitted fabric exhibits no waterabsorption extension rate and is remarkably uncomfortable when worn.

The polyamide fiber of Comparative Example 4 has a degree of orientationlower than 0.7. Therefore, the water absorption extension rate of thispolyamide fiber is excessively high, resulting in that the fabric madeof this fiber is remarkably uncomfortable when worn.

Example 7

Nylon-6 having a reduced viscosity of 1.80 dL/g (at a concentration of 1g/dL in orthoclorophenol at 30° C.) was used as a polyamide component(component A), and a thermoplastic modified polyvinyl alcohol (modifiedPVA) (product of Kuraray Co., Ltd. having a saponification degree of98.5, an ethylene content of 8.0 mol %, and a degree of polymerizationof 380) was used as the other component, i.e., the soluble component(component B). The components A and B were separately melted indifferent extruders, and a conjugated fiber having a cross section shownin FIG. 1 was injected through a multi-component fiber-spinning nozzlewith a ratio of nylon-6: modified PVA set to 70:30 (weight ratio).Subsequently, a thread injected through a spinneret was cooled using ahorizontal cooling air blower having a length of 1.0 m. Thereafter,water-free spinning oil including, as its components, an anti-staticagent and a lubricating agent was applied to the thread. The thread wasthen wound using a roller at a take-off speed of 3500 m/min. In thismanner, a conjugated fiber (111 dtex/24 filaments) was produced. Notethat the process steps of fiber production were performed smoothly. Theproduced conjugated fiber was knitted into cylindrical fabric by acircular knitting machine (28 gauge). The resultant knitted fabric wassubjected to a scouring step using hot water (90° C., 20 minutes) todissolve and remove the modified PVA.

In the same manner as in Example 1, the degree of orientation, themoisture absorption rate, the water absorption extension rate, and thecrimp extension rate of this polyamide fiber were measured, and theevaluation of knitted fabric of the fiber was performed through a weartest. The results of these measurements and evaluation are shown inTable 2.

Examples 8 and 9

A polyamide fiber of Example 8 was produced in the same manner as inExample 7, except that polyethylene terephthalate (copolymerized PET)having a limiting viscosity number [η] of 0.52 dL/g and copolymerizedwith 8 wt. % of polyethylene glycol having a molecular weight of 2000and 5 mol % of 5-sodium sulfoisophthalic acid was used as the componentB. A polyamide fiber of Example 9 was produced in the same manner as inExample 7, except that polylactic acid was used as the soluble component(component B), and a ratio of nylon-6: component B was set to 67:33. Thedegree of orientation, the moisture absorption rate, the waterabsorption extension rate, and the crimp extension rate of eachpolyamide fiber were measured, and the evaluation of knitted fabric ofeach fiber was performed through a wear test. The results of thesemeasurements and evaluation are shown in Table 2.

Examples 10 and 11

As shown in Table 2, a polyamide fiber of each of these examples wasproduced in the same manner as in Example 7, except that nylon-6,6(Example 10) or nylon-6/12 (Example 11) was used as the component A. Foreach fiber, the degree of orientation, the moisture absorption rate, thewater absorption extension rate, and the crimp extension rate weremeasured, and the evaluation of knitted fabric of each fiber wasperformed through a wear test. The results of these measurements andevaluation are shown in Table 2.

Examples 12 and 13

As shown in Table 2, a polyamide fiber of each of these examples wasproduced in the same manner as in Example 7, except that the conjugatedfiber was caused to have a cross section shown in FIG. 2 (Example 12) ora cross section shown in FIG. 3 (Example 13). For each fiber, the degreeof orientation, the moisture absorption rate, the water absorptionextension rate, and the crimp extension rate were measured, and theevaluation of knitted fabric of each fiber was performed through a weartest. The results of these measurements and evaluation are shown inTable 2.

Comparative Example 5

A conjugated fiber (size: 220 dtex) having a cross section shown in FIG.1 was injected through a multi-component fiber spinning nozzle, in thesame or similar manner to Example 7. Subsequently, a thread injectedthrough a spinneret was cooled using a horizontal cooling air blowerhaving a length of 1.0 m. Thereafter, water-free spinning oil including,as its components, an anti-static agent and a lubricating agent wasapplied to the thread. The thread was then taken off using a roller at aspeed of 1000 m/min., and drawn continuously without being wound. Thethread was drawn until its length became 2.5 times as long as theoriginal length, while being thermo-set at 150° C. In this manner, aconjugated fiber (110 dtex/24 filaments) was produced at a speed of 2500m/min. The produced conjugated fiber was knitted into cylindrical fabricby a circular knitting machine (28 gauge). The resultant knitted fabricwas subjected to a scouring step using hot water (90° C., 20 minutes) todissolve and remove the modified PVA. In this manner, the polyamidefiber of this comparative example was produced.

Next, the degree of orientation and the water absorption extension rateof this polyamide fiber were measured, and the evaluation of knittedfabric of the fiber was performed through a wear test, in the same orsimilar manner to Example 7. Note that the moisture absorption rate andthe crimp extension rate were not measured. The results of thesemeasurements and evaluation are shown in Table 2.

Comparative Example 6

A polyamide fiber was produced in the same manner as in Example 7,except that nylon-12 was used as the component A. The degree oforientation and the water absorption extension rate of this polyamidefiber were measured, and the evaluation of knitted fabric of the fiberwas performed through a wear test. Note that the moisture absorptionrate and the crimp extension rate were not measured. The results ofthese measurements and evaluation are shown in Table 2.

TABLE 2 Polyamide Soluble Conjugate Moisture Water Absorption EvaluationCrimp Component Component Ratio Cross Degree of Absorption ExtensionRate through Extension (Component A) (Component B) A:B SectionOrientation Rate (%) (%) Wear Test Rate (%) Example 7 Nylon-6 ModifiedPVA 70:30 FIG. 1 0.78 8 10 A 4.3 Example 8 Nylon-6 Copolymerized PET67:33 FIG. 1 0.84 6 5 B 3.4 Example 9 Nylon-6 Polylactic Acid 67:33 FIG.1 0.82 6 5 B 3 Example 10 Nylon-6.6 Modified PVA 70:30 FIG. 1 0.77 7 10A 5.6 Example 11 Nylon-6/12 Modified PVA 70:30 FIG. 1 0.75 5 7 B 4.7Example 12 Nylon-6 Modified PVA 70:30 FIG. 2 0.71 9 12 A 5.6 Example 13Nylon-6 Modified PVA 70:30 FIG. 3 0.8 6 8 A 2.5 Comparative Nylon-6Modified PVA 70:30 FIG. 1 — 4 1 C — Example 5 Comparative Nylon-12Modified PVA 70:30 FIG. 1 — 2 0 D — Example 6

As shown in Table 2, the polyamide fibers of Examples 7-13 have amoisture absorption rate equal to or higher than 5% at a temperature 35°C. and a humidity 95% RH, and a water absorption extension rate equal toor higher than 5% at a temperature 20° C. and a humidity of 65% RH. Thismeans that these polyamide fibers effectively control humidity, andknitted fabric made of these fibers is highly comfortable when worn.

On the other hand, the polyamide fibers of Comparative Examples 5 and 6have a moisture absorption rate lower than 5% at a temperature of 35° C.and a humidity of 95% RH, and a water absorption extension rate lowerthan 5% at a temperature of 20° C. and a humidity of 65% RH. This meansthat the fibers of these comparative examples control humidity lesseffectively and knitted fabric made of the fibers of these comparativeexamples is notably uncomfortable when worn, as compared to the fibersof Examples 7-13. In particular, nylon-12 used in Comparative Example 6is highly hydrophobic and has high crystal orientation among polyamideresin. Consequently, the fiber of Comparative Example 6 has a notablyreduced moisture absorption rate, as shown in Table 2, which means thatthe obtained knitted fabric exhibits no water absorption extension rateand is remarkably uncomfortable when worn.

INDUSTRIAL APPLICABILITY

The polyamide fiber of the present invention suitably absorbs andreleases moisture, and extends and contracts reversibly upon absorbingand releasing water. Therefore, a fiber structure containing thepolyamide fiber of the present invention exhibits a self-controlfunction by which the opening degree of stitches in the fiber structureis varied depending on absorption and release of water. Thus, thepolyamide fiber of the present invention may enable the production of ahighly comfortable fiber structure. The polyamide fiber of the presentinvention is highly suitable for the field of clothing, and exhibitsgood performance when used in sportswear, underwear, lining, pantyhose,socks, and other types of clothing.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1 Polyamide Component (Component A) in Conjugated fiber    -   2 Soluble Component (Component B) in Conjugated fiber    -   3 Hollow Portion in Conjugated fiber

1. A polyamide fiber having a degree of orientation equal to or higherthan 0.7 and equal to or lower than 0.85.
 2. The polyamide fiber ofclaim 1, having a moisture absorption rate equal to or higher than 5% ata temperature of 35° C. and a humidity of 95% RH, and a water absorptionextension rate equal to or higher than 5% at a temperature of 20° C. anda humidity of 65% RH.
 3. The polyamide fiber of claim 1, obtained byremoving, from a conjugated fiber containing a water-solublethermoplastic polyvinyl alcohol-based polymer and polyamide, thewater-soluble thermoplastic polyvinyl alcohol-based polymer by using hotwater.
 4. The polyamide fiber of claim 1, obtained by removing, from aconjugated fiber containing an easily alkali-soluble polyester-basedpolymer and polyamide, the easily alkali-soluble polyester-based polymerby alkali treatment.
 5. The polyamide fiber of claim 1, wherein thepolyamide is nylon-6.
 6. The polyamide fiber of claim 1, wherein thepolyamide fiber extends and contracts reversibly upon absorbing andreleasing water.
 7. A fiber structure, at least part of which is made ofthe polyamide fiber of claim
 1. 8. Clothing made of the fiber structureof claim
 7. 9. The clothing of claim 8, wherein the clothing isconfigured as at least one selected from the group consisting ofunderwear, sportswear, lining, pantyhose, and socks.